Project Summary Significance: There is an urgent need for novel approaches to treat or prevent Entamoeba histolytica as it is an important cause of diarrhea in infants in low income countries. There is no vaccine and only a single class of antiparasitics is effective for invasive amebiasis. Hypothesis: This project will test the hypothesis that metabolic products of the gut microbiome are capable of epigenetically altering the bone marrow to increase intestinal neutrophilic inflammation and provide antigen- nonspecific protection during subsequent ameba infection. Approach: This project will determine how the gut microbiome communicates with the bone marrow to regulate intestinal inflammation to subsequent infection. Preliminary data suggest that epigenetic changes in the bone marrow, caused by exposure to the intestinal bacteria Clostridium scindens, are sufficient to confer mucosal protection from subsequent Entamoeba histolytica infection. This finding led to the hypothesis that gut colonization with C. scindens increases a serum mediator (deoxycholate) that then acts on the marrow (JMJD3) to help support granulocyte monocyte progenitor (GMP) expansion and a more robust gut neutrophil response. Aim 1 will determine how C. scindens communicates from the gut to the marrow. Aim 2 and 3 will determine how the bone marrow is epigenetically altered during C. scindens colonization and protects from Entamoeba. Successful completion of these studies will identify how intestinal Clostridia communicate with the marrow to induce epigenetic changes that induce antigen-nonspecific ?trained innate immunity?. Additionally, the impact of our approach extends beyond amebiasis and infectious diseases to basic mechanisms of hematopoiesis and innate trained immunity. Successful completion of these studies will aid in development of next generation treatments that leverage the microbiome and trained immunity to help in clearance of pathogens or help modulate the severity of inflammation. Innovation: This work will provide a greater understanding of fundamental processes underlying trained immunity induced by the host microbiota. Novel concepts derived from this work will identify pathways important in microbiota-mediated protection from infection that can be targeted by translational medicine. The environment for this work is a research group and Division dedicated to the study of the pathogenesis of infectious colitis, including amebiasis, for the past 25 years. Extensive expertise in Epigenetics, Bioinformatics, and Clostridia biology is also included (see letters of support). Dr. Burgess, the project PI, is well cited in the field of trained immunity and pioneered study of the microbiome in regulating susceptibility to amebic colitis.